NORTHEASTERN FOREST EXPERIMENT STATION 

Upper Darby , Pennsylvania 

No* 34 

August 1954 

Do .Thinning And Prescribed Burning 

Affect The Growth Of Shortleaf Pine? 

In January 1946 a small study of thinning and prescribed burning was started in an old-field stand mostly of 

shortleaf pines about 38 years old, The stand is located on 

private land in Salem County, N. J. 

Four &acre plots were used in the study. On two of 

the plots a low thinning was made, removing 282 pines 2 to 7 

inches d.b.h. per acre. These amcunted to 34 percent of the 

original number of pines, or 20 percent of the basal area. 

In volume the cut amounted to 6.2 cords per acre in pines 

4 inches and larger. 

After the thinning, therewere 271 pines 4 to 11 

inches d.b.h. left on the thinned plots. On the unthinned 

plots there were 403 pines 2 to 10 inches d,b.h. 

During the 8 years after the thinning, two of the 

plots were prescribe-"burned three times. One of these plots 

had been thinned before burning; the other had not. Thus 

each of the four plots has had a different treatment. 

Thinning greatly reduced mortality during the 8 years 

' 

after treatment. On the thinned plots 9.4 to 9.7 percent of 

the pines died during that period; on the unthinned plots 

32.5 to 33 percent died. Thinning also increased the net 

volume growth of the pine overstory during this period. Net 

growth was 2.2 to 2.4 cords per acre more on the thirmed 

plots. *. 

Of course net groppth is influenced by the amount of 

mortality, as are changes in the diameter of the average 

tree. The average living tree on the unthinned plots increased 0.4 to 3.5 inch more in diameter in the 8--year periodthantheaveragetree onthethinnedplots. (~ossibly 

all of this conputed difference is because more small trees 

died, leaving the larger trees to be averaged on the unthinned plots . ) 
t 

Plot treatment Diameter Basal area Vollrme per acre 

per tree per acre 

Inches Sq.ft. Cu.ft. Cords 

Unthinned, unburned 0.5 11.7 461 5.5 

Unthinned, burned .6 13.7 53-4 6.2 

Thinned, unburned 5 11.0 436 5.4 

Thinned, burned .6 12- 7 509 6.1 

more than remove trees thk hill soon die-should affect the 

growthofthe future croptrees. To findout if it did, 

diameter and volume growth were computed for the 75 largest 

trees on each plot. In diameter growth (computed to the 

f 

Table 1.--Growth on 75 largest pine trees per plot 

during 8-year period 

nearest 1/10 inch), thinning did not affect these trees at 

all (table 1). In basal area, cubic feet, and cords the 

growth of these trees was slightly less on the thinned 

plots. 

In contrast, prescribed burning did favor both net 

growth of all pines and the growth of the largest pines. 

Net growth of all pines on the prescribe-burned plots was 

1.0 to 1.2 cords per acre more than on the unburned plots. 

When only the 75 largest pines'per plot are considered, the 

diameter growth per tree was 0.1 inch more on the burned 

plots; volume growth was 0.7 cord per acre more on the burned plots. 

While the effect of prescribed burning was quite cornparable for the two pairs of plots used in this study, further confirmation of this effect is needed before it can be 

accepted as universally true for the old-field pine stands 

ofsouthernNewJersey. Suchconfirmationmaybeobtained 

within a few years from a more thorough study that has been 

started recently in sapling-pole pine stands. 

--Ha A. SOMES and G. Re MOORHEAD 

Agriculture-Forest Service-Upper Darby